1. Field of the Invention
The present invention relates to a recording medium that is suitable for ink jet recording, and particularly relates to a recording medium that is superior in absorption and color development of aqueous inks as well as in storage stability of recorded images. The present invention also relates to a recording method in which the recording medium is employed.
2. Related Background Art
Recording mediums for ink jet recording heretofore known include:
(1) those made by sizing of general paper mainly composed of pulp to a low degree into articles like filter paper or blotting paper,
(2) those made by providing an ink absorbing layer with a porous inorganic pigment on a base paper, such as general wood-free paper, having low ink-absorbency as described in Japanese Patent Application Laid-open No. 56-148585, and the like.
In ink jet recording for forming color images of high quality and high resolution, particularly high image storability is required. To meet such requirements, methods are known that reduce fading of images caused by irradiation of visible light or ultraviolet light like sunshine (see, for example, Japanese Patent Applications Laid-open Nos. 60-49990, No. 61-57380, etc.).
Recently, however, indoor discoloration of recorded images has become an important problem peculiar to coated paper.
This is different from the usual problems of light resistance which relate, for example, to fading of images by irradiation of ultraviolet light or visible light that occurs in images formed on any kind of paper including general PPC paper, wood-free paper, coated ink-jet-recording paper, and the like. On the contrary, the indoor discoloration of images discussed in the present invention occurs on coated paper stored, for example, in absence of direct sunlight irradiation, but does not occur in images printed on non-coated paper like PPC paper, which is different from the above mentioned problems on light resistance.
As mentioned above, the indoor discoloration is peculiar to coated paper. Accordingly, the indoor discoloration is considered to be caused by a pigment in the coat layer. The indoor discoloration is known to be dependent on the specific surface area of the pigment employed. Although the discoloration is retarded by use of an ordinary paper-filler, such as calcium carbonate, kaolin, talc, and the like having a smaller specific surface area, the use of such a filler involves the problems that the resulting image density is low, and high quality and high resolution of the image cannot be achieved. On the contrary, the coated paper comprising silica having a larger surface area and a higher activity as disclosed in Japanese Patent Application Laid-open No. 56-185690 involves the disadvantage of significant indoor discoloration although it gives images of high optical density.
As discussed above, the suppression of the indoor discoloration is inconsistent with an increase of image density, which could not be solved by the prior art.